Liquid crystal display devices are widely used as a display device of smartphones, tablet computers, vehicle-navigation systems, etc. In general, a liquid crystal display device comprises a liquid crystal display panel and a planer illumination device (backlight device) overlaid on the rear surface of the liquid crystal display panel and illuminates the liquid crystal panel. The backlight device comprises a reflective layer, a light guide plate (light guide), an optical sheet (a prism sheet or a diffusion sheet), an LED as and a light source, etc. The reflective layer and the optical sheet are stacked one on another.
Meanwhile, such a liquid crystal display is proposed that the display screen is partially or entirely inclined or curved. In such a liquid crystal display device, the backlight device is also partially or entirely inclined or curved.
The viewing angle characteristics of a liquid crystal display device are dependent on the viewing angle characteristics of the backlight device. In many cases, the backlight device is adjusted so as to exhibit its maximum luminance in a normal direction to the light-emitting surface. That is, high-intensity light is emitted to a front direction in a flat region and to an oblique direction in an inclined region (curved region). Therefore, when the display screen is observed from the front direction, a significant difference in luminance is created between the flat region and the inclined region or curved region of the display screen, thereby degrading the display quality.
Here, when a high-haze diffusion sheet (in-plane uniform haze) is placed on the outermost surface of the emission face of the backlight device, frontal luminance of the inclined region increases and front luminance of the flat region decreases. In this manner, the difference in luminance between the flat region and the inclined region can be lessened to improve reduced, thereby improving the display quality. However, in this case, the luminance of the flat region decreases to degrade the commodity value itself.